Two-dimensional test problem for neutron-physics calculation of the WWER cores

Calculation of power in FA fuel rods is an important element in safety justification of the operating reactors and those under design. Traditionally in Russia and abroad the calculations of neutron physics characteristics (in particular, assembly-by-assembly and fuel rod-by-fuel rod power distributions) are performed in diffusion approximation. This approach provides for rather quick and accurate calculation of neutron physics characteristics. However there is a number of problem areas (core periphery, CPS CR assemblies, etc.) wherein the diffusion approximation has a high methodical error. On the one hand, the power in fuel in these areas is low and not important for safety justification with the conservative approach. On the other hand, increase in WWER competitiveness requires use of realistic approximation. Accuracy of calculations of fluence to the RPV, abrupt changes of power in fuel rods, adjacent to absorbing element, under their withdrawal from the core, as well as other important aspects are related directly to the issue considered in the report. To improve the accuracy of calculation of power in the mentioned problem areas using the method of diffusion approximation the methodical corrections can be used and their usage is considered in the given report. The work is performed within the frame of code package Sapfir95 and RC. In the comparative analysis the precision code MCNP5 is used that solves the equation of neutron transport by Monte-Carlo method (Authors)